Composite laminate for sliding elements having a running or sliding layer to which a conforming filler-containing layer is applied

ABSTRACT

A lacquer coating is applied to a laminated metal composite forming a sliding element such as a plane bearing and has particles of solid lubricants incorporated therein to form islets of greater thicknesses than the surrounding film and which serve as lubricant-trapping surface formations. The particles may be of polytetrafluoroethylene, fluorinated graphite or molybdenum disulfide and the lacquer is preferably an epoxy resin-based lacquer.

FIELD OF THE INVENTION

My present invention relates to a composite laminate for slidingelements and to a method of making same. More particularly, theinvention relates to a two-layer or three-layer composite having ametallic sliding layer, generally of an aluminum alloy, and a conforminglayer on a free surface thereof engaging the surface which is to slideon the composite or upon which the composite is to slide.

BACKGROUND OF THE INVENTION

When I refer to "sliding elements" herein or use terminology of similarimport, I intend thereby to describe a structure which is intended inmachine applications and the like to slide upon another structure orupon which another structure is intended to slide. Typical of suchsliding elements is a plain bearing or sleeve bearing which may receivea shaft or rod which is intended to rotate or reciprocate in thatbearing with a sliding surface of the shift or rod in direct contactwith the free surface of the sliding element. Similar principles areused in linear sliding structures. For example, the tailstock orlongitudinal slide or cross slide of a lathe or other machine tool mayslide longitudinally on guideways of a bed or other part of the machinetool. Either the body which slides or the stationary body, for example,the bed, may then be provided with a sliding element in accordance withthe invention since there is a sliding engagement of a moving part witha stationary part in a linear direction in these systems. The slidingelements of the invention can, therefore, be used whereever two machineparts are to slide on one another and one of these parts is to have alow friction reduced-wear surface. Where reference is made herein to aconforming layer, or terms of a similar import are used, I intendthereby to describe a layer which has slight deformability when theparts are brought together and are in sliding contact to conform to thesurface of the part riding on the sliding element or on which thesliding element rides and which also conforms to the surface of thesliding element to which that layer is applied.

From German Patent Document DE-OS 22 06 400 and German Patent DocumentDE-OS 27 07 041, composite structures for slide elements are describedin which polymer compounds with friction reducing or sliding improvingadditives are applied to the sliding layer of the composite or as thesliding layer to form the composite. It is also known to apply solidlubricants for the direct formation of a lubricant film in the form ofpowder or pastes to such sliding elements.

However, these techniques can yield effective results only when thesurfaces which are juxtaposed and are to slide relative to one anotherhave been properly prepared by mechanical means, for example, brushing,sand blasting or other roughening techniques, to provide contours whichtrap the friction and wear reducing materials or the surfaces areprovided with a sintered structure or otherwise formed with grooves,recesses or depressions to accommodate the lubricant materials. Suchtechniques are time consuming and expensive and are not alwayspractical.

OBJECTS OF THE INVENTION

It is, therefore, the principal object of this invention is to providean improved composite for the purposes described so that the materialbetween the sliding surfaces is more uniformly loaded, betterdistributed and retained in place more effectively so that an overallimprovement in the quality of the sliding element is obtained.

Another object of the invention is to provide a low cost sliding elementor plane bearing structure which is free from the drawbacks of earliersystems.

Still another object of the invention is to provide an improved methodof fabricating a slide element with advantages over prior art slidingelements, at substantially lower cost.

SUMMARY OF THE INVENTION

These objects and others which will become apparent hereinafter areattained, in accordance with the invention in a two-layer or three-layercomposite structure in which, for example, an aluminum alloy slidinglayer is applied to a support layer, e.g. of steel, and a conforminglayer is applied to the sliding layer. According to the invention, theconforming layer comprises a film-like thin coating of a sliding lacquercontaining disposed therein a filler which improves the slidingcharacteristics and which has over the greater part of its area a basicthickness of at most 10 micrometers and having nonuniformly distributedlocal regions in a fleck-like or islet pattern of greater thickness,preferably containing the filler.

These regions of greater thickness, which may appear as dark flecks in akind of leopard spot pattern in the otherwise thin layers of thelacquer, the solid friction reducing materials can be contained. Therises provide a synthetic surface roughness which, in tribologicalsystems provides improved retention of lubricants, especially liquidlubricants.

With wear of the high points, the friction reducing solids constitutingthe fillers are liberated, thereby improving the sliding characteristicsof the slide element with use.

Apart from the functional advantages afforded by the invention,therefore, there is also a significant reduction in the cost of makingthe slide element since the materials used are of low cost and it ispossible to apply the conforming layer at low cost and without the needfor expensive surface treatments of the metal surface.

In a preferred embodiment of the invention, the thin-film lacquercoating has a basic thickness between 2.5 micrometers and 6 micrometers,preferably between 3 micrometers and 5 micrometers, while the thicknessregions have a thickness of say 10 micrometers.

The solid fillers which improve the sliding characteristics can beprovided as fine particles with thicknesses of up to 10 micrometers andpreferably are trapped in the thickened regions of the slide lacquercoating.

The sliding lacquers can be composed of a soluble polymer, for example,an epoxy resin, and the feeling can be constituted from pulverulentlubricants, for example, polytetrafluoroethylene and/or fluorinatedgraphite and/or molybdenum disulfide. The sliding lacquer coating ispreferably bound into or baked onto the free surface of the slidinglayer.

According to the method aspect of the invention, a two-layer orthree-layer composite with a metallic sliding layer, e.g. of an aluminumalloy, has its free surface degreased but otherwise untreated, i.e. nottreated by another roughening technique.

The degreased surface is provided with a film forming thinned layer of adispersion of the solids capable of improving the sliding properties ina polymer solutions so that fleck-like thickened areas are formed in thecoating upon the drying, setting or cross linking of the polymer in thecoating.

The so formed nonhomogeneous film is then heated to a temperature of100° C. to 250° C. to bake the coating into the metal surface andthereby complete the thermosetting of the polymer and encapsulate thesolids in the film. The use of a dispersion of a polymer solution andthe filler particles thus may allow a uniform thickness of the coatingto be applied to the metal surface. As a result of solvent loss andincreasing setting, however, the lacquer layer thickness reduces so thatthe fleck-like regions or rises emerge. By controlling the process, itis possible to determine the relative thicknesses of the base layer andthe rises.

This effect is most reliably obtained and is most strongly observed whenthe attached coating thickness is substantially equal to or slightlygreater than the maximum thickness of the particles dispersed in thedispersion and when solidification, drying takes place immediately aftercoating of the dispersion onto the metal surface. It appears that thisthickness results in a local contraction of the solid particles togetherin the fleck regions or rises and that this phenomenon occurs before thecoating and the various regions thereof are fully anchored to thesurface which is coated.

The thickness reduction of the lacquer matrix is preferably effected bycarrying out a precrosslinking of the lacquer matrix by the applicationof an elevation temperature for a specific time interval immediatelyafter coating.

The application of the sliding lacquer coating can be effected in asimple manner. For example, the lacquer can be sprayed onto the metalsurface. It is also possible to utilize roller or blade doctoringtechniques to apply the dispersion. The dispersion can be formed bymixing fine particles of polytetrafluoroethylene and/or fluorinatedgraphite and/or molybdenum disulfide to an epoxy resin in a solvent forevaporation at the temperature given.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of my inventionwill become more readily apparent from the following description,reference being made to the accompanying highly diagrammatic drawing inwhich:

FIG. 1 is a cross sectional view through a composite sliding elementaccording to the invention enlarged in scale;

FIG. 2 is a view in the direction of arrow 2 of FIG. 1 to a still largerscale;

FIG. 3 is a section taken along the line III--III of FIG. 2; and

FIG. 4 is a diagram illustrating the steps in the production of thecomposite element of FIGS. 1 and 3.

SPECIFIC DESCRIPTION AND SPECIFIC EXAMPLE

FIG. 1 shows a laminated structure 10 forming a sliding elementaccording to the invention which can be, for example, a connecting rodbearing for a diesel engine.

The laminated composite 10 comprises a support layer 11 of steel and asliding layer 12 of an aluminum alloy of, for example, typeAlZn5Si2CuPb. This sliding layer 12 is formed on its upper surface witha conforming layer 13 which is described in greater detail below.

As FIGS. 2 and 3 show, the conforming layer 13 is constituted of afilm-like thin coating 14 of a sliding lacquer in which solid particlesof a sliding-promoting substance 15 is received. The particles 15 aretrapped in the lacquer matrix 16.

The greater part of the area of the coating 14 (see FIGS. 2 and 3) has arelatively small basic thickness 17 which can correspond to thethickness of the firm without the solids. This basic thickness can bebetween 3 micrometers and 5 micrometers and can vary between them.

From this layer of basic thickness project in a fleck pattern, islets 18which represent rises or elevated regions which are nonuniformlydistributed and are of nonuniform size. They can have, however, agreater thickness than the thickness 17 and have been represented ashaving the thickness 19 which may be about 10 micrometers.

As is apparent also from FIG. 3, the fine particles 13 can have aparticle size or thickness of up to 10 micrometers themselves althoughthey may have substantially lower particle sizes as is also apparentfrom FIG. 3 and can gather in the islets. The lacquer coating 14 isbaked into the free surface of the sliding layer 12. It can comprise, inthe specific example, an epoxy resin containing up to 15% by weight of amixture of equal parts of polytetrafluoroethylene, fluorinated graphiteand molybdenum disulfide particle. The minimum particle size of theseparticles may be 5 micrometers and the maximum particle size about 10micrometers as noted.

In FIG. 4 I have shown a preferred method of making the sliding elementof FIGS. 1 to 3.

In step of FIG. 4 I have shown a spray device 20 which is spraying apreviously prepared dispersion of the dissolved polymer and solidparticles onto the free surface of the sliding layer 12 of the laminatedbody 10. The thickness of the spray dispersion layer 21 is between 10and 15 micrometers so that even the thickest particles 15 are fullyimmersed in the polymer solution. Because of the surface temperature ofthe polymer solution, namely, the epoxy resin, a substantially smoothsurface is formed on the dispersion layer 21.

Directly following the spray of the dispersion layer 21 on the aluminumlayer 12, the dispersion layer is heated to 100° C. for a period ofseveral minutes as represented by step b utilizing a radiant heater 22.There results a precrosslinking of the lacquer matrix which gives riseto a shrinkage of the latter and to a certain extent one can observe theislets being formed as the solid particles tend to come together andprotrude above the remainder of the lacquer matrix.

The incipient islet rises are represented at 18 in step b of FIG. 4.

After this brief precrosslinking of the lacquer matrix, the compositecan be stored for some time and, if desired, can be shaped by bending orother techniques to form bearing shells or bushings.

In steps c and d, baking of the lacquer layer 14 into the surface of themetal layer 12 is effected at a temperature of 100° C. to 250° C. in thetunnel oven 23. The baking and hardening step results in a furthershrinkage of the lacquer matrix so that the islets 18 are now seen to bemore prominent and to have the configuration shown in FIGS. 1 through 3.

Tests of the product, utilizing it as a radial bearing in a radialbearing test stand in which the effect is similar to that which applieswhen the bearing forms the connecting rod bearing in a diesel engine,were carried out. In all of the test examples, the sliding metal layer12 was an aluminum alloy of type AlZn5Si2CuPb, the lacquer was an epoxyresin and the particles were composed solely of polytetrafluoroethylene.Otherwise the method used and the parameters used were those described.The lacquer coating was able to withstand 250 hours of running at aspeed of 4000 rpm at a full load of 70N/mm² after which the surface wasfound to be smooth and completely free from discontinuities.

For comparative purposes, a similar test sample without the lacquercoating with a load of only 60N/mm² in the same time period, showedcracks and broken pieces. The test results demonstrated surprisinglyeffective running properties for the lacquer coating 14 at high loadswith low wear.

I claim:
 1. A multilayer composite sliding element, comprising:a metalsliding layer having a sliding surface; and a conforming layer on saidsurface, said conforming layer comprising a thin film coating of alacquer containing sliding-promoting solids in the form of fineparticles and in which nonuniformly distributed islets are received,wherein said particles are predominantly located in said islets, saidlayer conforming having over a major part of an area of said slidingsurface a basic thickness of ≦10 μm, said islets having a greaterthickness than said basic thickness.
 2. The sliding element defined inclaim 1 wherein said thin film coating has a thickness of 2.5 μm to 6 μmand said greater thickness is about 10 μm.
 3. The sliding elementdefined in claim 2 wherein said thin film coating has a thickness of 3μm to 5 μm.
 4. The sliding element defined in claim 2 wherein saidsolids are in the form of fine particles have a thickness of ≦10 μm. 5.The sliding element defined in claim 4 wherein said lacquer is composedof a soluble polymer and said solids are a pulverulent lubricant.
 6. Thesliding element defined in claim 5 wherein said polymer is an epoxyresin and said pulverulent lubricant is selected from the group whichconsists of polytetrafluoroethylene, fluorinated graphite, molybdenumdisulfide and mixtures thereof.
 7. The sliding element defined in claim6 wherein said lacquer is baked into said surface.